What was the scoop on UN aid convoy attack in Syria?

The damage signature on UN aid convoy trucks points is baffling. It is difficult to determine whether it was the result of aerial bombardment or ground-based artillery or arson attack. If aerial attack scenario is considered, then either Syrian or American involvement is suspect since Russians claim radar data of a Predator drone that carries hellfire missile. Russian drone footage shows Al-Nusra driving a heavily armored vehicle driving past the UN aid convoy using the aid convoy as cover. These Western-Gulf sponsored militants are alleged to be using aid convoys to transfer heavy arms supplies. Even the UN officials rejected request from the Syrian govt to inspect the contents of those convoys - very suspicious !